If the EPA’s Air Quality Index measures more than 150—or 100 if you have asthma or other sensitivities—adjust your workout by doing the following.

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Bad-air days hit their peak in the summer months
Photo: Jordan Clark Haggard

STEER CLEAR OF BUSY STREETS: Pollution drops considerably the farther you move from congested roadways. Just 200 yards away, levels are as much as four times lower. Trees can offer protection, too.

START EARLY:Ozone, a key component of smog, is produced when sunlight reacts with pollutants, so levels rise steadily throughout the day—and are at their highest in the summer months. Get your run in first thing in the morning.

GET MORE ANTIOXIDANTS: In theory, antioxidant supplements should help guard against pollution-induced oxidative damage. The jury’s still out on whether they do, but it can’t hurt to eat more antioxidant-rich fruits and vegetables, such as broccoli, red peppers, and melon.